Fire resistant plastic pallet

ABSTRACT

A fire resistant plastic pallet comprises greater than or equal to 65 wt. % high density polyethylene; and a sufficient amount of intumescence additive material to impart fire resistant properties to the fire resistant plastic pallet such that the fire resistant plastic pallet is capable of passing a fire test standard consistent with UL 2335, wherein weight percents are based on a total weight of the fire resistant plastic pallet.

BACKGROUND

Pallets are portable platforms used for handling, storing or moving materials and heavy packages in, for example, warehouses or during shipping. Traditionally, pallets have been made of wood, which can harbor bacteria and other contaminants. As such, it has been proposed to replace wood pallets with plastic pallets. Plastic pallets are required to meet or exceed the fire resistance standards set for wood pallets. The standards include requirements that the material should have low heat release rate, low flame spread rate, and should maintain strength during fire exposure.

A plastic that can be used in pallets is polyethylene, because it is strong, has a high toughness, and is inexpensive. Polyethylene, however, can melt, drip and burn when exposed to fire. Dripping can contribute to the fast spread of fire. The heat release rate during fire is also large for polyethylene. Polyethylene itself will not be able to pass the UL 2335 fire test, which is aimed at measuring fire resistance of stacked pallets.

There thus remains a need for fire resistant materials for use in plastic pallets and other applications requiring fire resistant plastics.

SUMMARY

Disclosed herein are fire resistant plastic pallets.

One embodiment of a fire resistant plastic pallet comprises greater than or equal to 65 wt. % high density polyethylene; and a sufficient amount of intumescence additive material to impart fire resistant properties to the fire resistant plastic pallet such that the fire resistant plastic pallet is capable of passing a fire test standard consistent with UL 2335, wherein weight percents are based on a total weight of the fire resistant plastic pallet.

On embodiment of a fire resistant pallet comprises about 65 wt. % to about 80 wt. % high density polyethylene; about 20 wt. % to about 35 wt. % intumescence additive material, wherein the intumescence additive material comprises a gas-generating foaming agent, a char-forming agent, and a filler; and wherein weight percents are based on a total weight of the fire resistant pallet.

The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:

FIG. 1 is a cross-sectional view of an exemplary embodiment of a fire resistant laminate comprising an intumescent plastic layer and a non-intumescent polymer layer.

FIG. 2 is a cross-sectional view of an exemplary embodiment of a fire resistant laminate comprising an intumescent plastic layer, a non-intumescent polymer layer, and an adhesive layer.

FIG. 3 is a cross-sectional view of an exemplary embodiment of a fire resistant laminate comprising a first intumescent plastic layer, a non-intumescent polymer layer, and second intumescent plastic layer.

FIG. 4 is a cross-sectional view of an exemplary embodiment of a fire resistant laminate comprising a first intumescent plastic layer, a first adhesive layer, a non-intumescent polymer layer, a second adhesive layer, and a second intumescent plastic layer.

DETAILED DESCRIPTION

Fire resistant blends and fire resistant laminates are disclosed herein for use as a fire resistant pallet. The blends may employ an intumescent plastic or an intumescence additive(s) that is blended with a non-intumescent polymer that is compatible with, or can be made compatible with, the intumescent plastic or intumescent material. By compatible, it is meant that the polymers are miscible when blended or can be rendered miscible by the addition of a compatibilizing agent. The laminates comprise a layer comprising an intumescent plastic and an adjacent layer comprising a non-intumescent polymer. As used herein, the term “intumescent plastic” refers to a material that first expands and then chars when exposed to fire to produce a heat resistant barrier that can reduce the rate of heat transfer to nearby objects and also reduce the spread of fires. Additionally, it is noted that the phrase “sufficient to impart fire resistant properties” is used throughout this disclosure to refer to fire resistant blends and fire resistant laminates that are capable of passing a fire test standard consistent with UL 2335 when the fire resistant blends and fire resistant laminates are used to produce a pallet. It is noted that a fire test standard for pallets included, but is not limited to, those standards promulgated by the National Fire Protection Association (NFPA), Underwriters Laboratories Inc. (UL) (e.g., UL 2335), Factory Mutual Research Company (FMRC), and National Association of Fire Marshals. It is to be understood that the fire resistant pallets disclosed herein are capable of passing a comparable test to UL 2335 as set forth by various associates and the like, which are similar to those described above.

It should further be noted that the terms “first,” “second,” and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. Furthermore, all ranges disclosed herein are inclusive and combinable (e.g., ranges of “up to about 25 weight percent (wt. %), with about 5 wt. % to about 20 wt. % desired, and about 10 wt. % to about 15 wt. % more desired,” is inclusive of the endpoints and all intermediate values of the ranges, e.g., “about 5 wt. % to about 25 wt. %, about 5 wt. % to about 15 wt. %,” etc.).

An intumescent plastic is a blend comprising a resin matrix, a heat stabilizer for the resin matrix, and intumescence additives. The intumescence additives include gas-generating foaming agents, char-forming agents, fillers, and combinations comprising at least one of the foregoing additives.

Preferably, the resin matrix of the intumescent plastic comprises a polyethylene (e.g., high density polyethylene), chlorinated polyethylene, and combinations comprising at least one of the foregoing resins. For example, in an embodiment, the polyethylene preferably is a high density polyethylene (HDPE) having a density of about 0.940 to about 0.970 grams per cubic centimeter (g/cm³). Generally, these HDPEs are available with a number average molecular weight of about 10,000 atomic mass units (amu) (usually waxes) to ultra high molecular weight HDPE (UHMW-HDPE) of several million.

Different grades of high density polyethylene can be employed depending on the application and the method of processing. For example, high molecular weight/high melt viscosity grades are used for blow molding applications. Low melt viscosity grades are desirable for injection molding. Extrusion is generally performed using intermediate melt viscosities. One measure of melt viscosity is the melt flow index conducted per ASTM D1238 test procedure. Melt index is the amount of molten resin, in grams, that flows through a standard diameter capillary in a ten minutes period, when the melt is heated to 190° C. and is subjected to a load of 2,160 grams. It is noted that melt flow index is inversely related to melt viscosity. Injection molding grades of polyethylene preferably have a melt index of about 10 grams per 10 minutes to about 50 grams per 10 minutes, where extrusion grades preferably have a melt index of about 15 grams per 10 minutes to about 0.5 grams per 10 minutes. Furthermore, blow molding grades preferably have a melt index of about 2 grams per 10 minutes to about 0.2 grams per 10 minutes, with a melt index of less than 0.2 grams per 10 minutes possibly obtained.

The chlorinated polyethylene (CPE) used as the resin matrix of the intumescent plastic preferably comprises about 36 percent by weight (wt. %) to about 42 wt. % chlorine, wherein weight percent based on the total weight of the CPE. A suitable commercial example of CPE is TYRIN® 3615P available from DuPont Dow Elastomers Co., Midland, Mich., containing 36 wt. % chlorine based on the total weight of the CPE. It is noted that the CPE can be combined with HDPE at different ratios to produce moldable intumescent thermoplastic elastomer grades with varying degrees of hardness. CPE can also be formulated into an intumescent material without HDPE through the addition of a small concentration of cross-linking agents, as discussed in greater detail below. The intumescent material formed can be highly elastomeric and can act as an efficient noise and vibration isolator, especially if the material is foamed during processing.

In other embodiments, HDPE may be mixed with CPE and/or silicone rubber. An advantage of using silicone rubber is that during burning, less smoke is evolved compared to materials that do not include silicone rubber. In embodiments having no CPE, it is noted that no chlorinated gaseous products may be produced as burning products of the intumescent material.

In other embodiments, the resin matrix of the intumescent plastic comprises a chlorinated polymer such as a chlorinated polyethylene optionally mixed with polyvinyl chloride, high density polyethylene, or a combination comprising at least one of the foregoing components.

Furthermore, in various other embodiments, the resin matrix of the intumescent plastic comprises a high density polyethylene mixed with a chlorinated polyethylene and a silphenylene siloxane elastomer. Suitable silphenylene siloxane elastomeric polymers include those based on, for example, 1,4-phenylene-hexamethyltrisiloxanyl monomer or 1,4-phenylene-1,1,3,5,5-pentamethyl-3-vinyltrisiloxanyl monomer are suitable provided that the polymers are of sufficient molecular weight to provide the desired physical and intumescent properties to the molded composition.

In yet another embodiment, the resin matrix of the intumescent plastic comprises a recycled polyethylene and a chlorinated polyethylene. Suitable resin matrixes include those discussed in U.S. patent application Ser. No. 10/055,112 to Abu-Isa and U.S. patent application Ser. No. 09/632,989 to Abu-Isa et al. The recycled polyethylene may be obtained, for example, from scrap generated during the manufacturing of plastic fuel tanks or from regrind obtained from post consumer plastic fuel tanks, milk bottles, garbage bags, or other plastic containers made of polyethylene.

In addition to the resin matrixes discussed above, the intumescent plastic comprises a heat stabilizer that is compatible with HDPE and/or CPE. Preferably, the heat stabilizers include, for example, thioesters such as distearylthiodipropionate (DSTDP) and a butylated reaction product of p-cresol and dicyclopentadiene (WINGSTAY L), which is a very effective hindered phenol antioxidant, and combinations comprising at least one of the foregoing heat stabilizers. It is noted that distearylthiodipropionate is commercially available as DSDTP from Witco Corporation, Greenwich, Conn., and the phenol is available as WINGSTAY L from R.T. Vanderbilt, Norwalk, Conn. In addition to these heat stabilizers, magnesium oxide may be employed to absorb evolved HCl produced during aging of chlorinated polyethylene and thus act as an effective dehydrochlorination stabilizer. Other heat stabilizers include hydroquinone derivatives, organic phosphite heat stabilizers such as tetraphenyl dipropylene glycol diphosphate, and amine antioxidants, and combinations comprising at least one of the foregoing heat stabilizers.

As briefly noted above, the intumescence additives of the intumescent plastic include gas-generating foaming agents and char-forming agents and combinations comprising at least one of the foregoing additives. Gas-generating foaming agents are used in the compositions to generate gases in order to foam the resin matrix before it is consumed by fire. Two desirable gas-generating agents are ammonium dihydrogen phosphate, NH₄H₂PO₄, ammonium polyphosphate (NH₄PO₃)_(n), and combinations comprising at least one of the foregoing agents, which emit ammonia when heated. Hydrated alumina, hydrated magnesia, and combinations comprising at least one of the foregoing agents are also desirable, because they emit water vapor when heated. It is noted that the ammonium dihydrogen phosphate can also form phosphoric acid, which may act as a catalyst to encourage char formation from polyhydroxy compounds. Preferably, the intumescent plastic comprises at least one of ammonium dihydrogen phosphate and ammonium polyphosphate, and at least one of hydrated alumina, hydrated magnesia and melamine, or combinations comprising at least one of the foregoing gas-generating foaming agents.

Char-forming agents for the intumescent plastic include starch (e.g., corn starch) or other carbohydrates that form heavy char when exposed to fire. Polyhydric alcohols such as trihydroxy alcohols and tetrahydroxy alcohols, and combinations comprising at least one of the foregoing alcohols, may also perform the same function. Preferably, char forming agents are selected from the group consisting of monopentaerythritol, dipentaerythritol, and combinations thereof comprising at least one of the foregoing char-formers. For example, a desirable char formation agent is a blend of monopentaerythritol and dipentaerythritol, which is commercially available as PERSTORP PE from Perstorp Compounds, Inc., Florence, Mass.

Other optional ingredients may be added to the intumescent plastic. A filler such as, for example, glass fibers, mica particles, titanium oxide powder, and combinations comprising at least one of the foregoing fillers, may be added to help strengthen the composition and develop a strong structure of the material after intumescing. Glass fiber reinforcing filler lead to increased strength in the structure of the intumescent material after burning. Other fillers that can also provide strength to the residue are titanium dioxide, graphite, mica, and combinations comprising at least one of the foregoing fillers. Antimony oxide and/or zinc borate may also be added to impart fire retardancy to the intumescent plastic and slow down the burning process. This effect is helpful in decreasing heat release rate during fire and increasing the char content.

The intumescent plastic can comprise a blend employing about 25 wt. % to about 60 wt. % of the resin matrix component, about 5 wt. % to about 15 wt. % of the heat stabilizer component, and about 25 wt. % to about 40 wt. % of the intumescence additives. For example, an exemplary intumescent plastic composition is shown in Table 1. It is noted that the weight percents illustrated in Table 1 are based on the total weight of the intumescent plastic. TABLE 1 Composition of Intumescent Plastics Preferable Component Wt % Example, Wt % High density polyethylene 0-60 15-25  Chlorinated polyethylene 0-60 27-33  Chlorowax 0-15 5-10 Ammonium dihydrogen phosphate 0-15 7-15 Hydrated magnesium oxide 0-30 9-17 Hydrated aluminum oxide 0-30 9-17 Distearylthiopriopionate 0-5  0.5-5   Hindered phenol 0-5  0.5-5   Chopped glass fiber 0-20 2-20 Antimony oxide 0-10 2-5  Pentaerythritol, mono- and di- 3-10 3-5  Graphite 0-15 5-10

Other specific examples of exemplary intumescent plastic compositions are shown in Table 2. In those examples, the intumescent plastic comprises a resin matrix comprising recycled polyethylene. It is noted that the weight percents illustrated in Table 1 are based on the total weight of the intumescent plastic. TABLE 2 Compositions Comprising Polyethylene Wt % Composition Composition Composition Component 1 2 3 Recycled high density 23 23 23 polyethylene Chlorinated polyethylene 30 30 30 Silicone 0 2 2 Chlorowax 7 5 5 Ammonium dihydrogen 8 7 7 phosphate Hydrated magnesium oxide 2 16 16 Hydrated alumina 15 0 0 Distearylthiopriopionate 0.5 0.5 0.5 Hindered phenol 0.5 0.5 0.5 Chopped glass fibers 6 6 6 Antimony oxide 3 5 5 Titanium dioxide 0 2 2 Pentaerythritol 5 3 2.9 Dicumyl peroxide 0 0 0.05 Trimethylolpropane- 0 0 0.05 trimethylacrylate

Other specific examples of intumescent plastics are shown in Table 3. TABLE 3 Other Intumescent Plastics Wt % Compo- Compo- Compo- Compo- sition sition sition sition Component 4 5 6 7 High density polyethylene 10 5 5 0 Chlorinated polyethylene 45 50 50 38 Chlorowax 7 7 7 8 Ammonium dihydrogen 8 0 4 0 phosphate Hydrated magnesium oxide 15 15 15 25 Distearylthiopriopionate 0.5 0.5 0.5 1 Hindered phenol 0.5 0.5 0.5 1 Antimony oxide 5 5 2 9 Pentarythritol, mono- 5 5 5 0 and di- Graphite 4 12 11 9 Chopped Glass 0 0 0 9

The intumescent plastics can be mixed on a laboratory scale by different methods including, for example, mixing on a two-roll mill heated to about 65° C. The polymeric resin or resins and the stabilizers may be added to the rolls and shear mixed for about five minutes. At that time suitable mixing may be visually observed and the material may be banded on one of the rolls. The actual temperature of the resin during mixing may approach about 150° C. due to shearing of the mixture. The remaining ingredients except filler may be added in a fine powder form and mixed well with the resin. The filler may then be added and mixed into the formulation for several minutes. The total mixing time of each compound may be greater than or equal to 15 minutes.

In other embodiments, formulations may also be prepared by mixing in a Brabender bowl, which is a small internal mixer, and in a large Banbury internal mixer. For example, the Banbury cavity may be preheated to about 93° C. Then, a first batch of ingredients is added to the bowl. These ingredients include (for example) chlorinated polyethylene and high density polyethylene, hydrated magnesium oxide, hydrated alumina, DSTDP, antimony oxide, corn starch and chlorowax. The mixing speed of the bowl may then be increased to, for example, about 120 revolutions per minute (rpm), and the ingredients allowed to mix for about two to three minutes. When using HDPE, the temperature of the mix may be permitted to rise to about 120° C. to about 140° C. to melt the polyethylene and incorporate it into the mixture. Following this first mixing operation, a second batch of ingredients which may include, for example, ammonium dihydrogen phosphate and glass may be added to the bowl, with mixing continued for about three more minutes or until the temperature reached about 160° C., whichever first occurs. The mix may then be removed from the bowl and dumped onto a mill to further mix and sheet out the composition. The temperature of the mill may be about 132° C.

Another example of intumescent composition mixing that is suitable involves a Brabender extruder. The temperatures of the three extruder barrel zones and the die may be varied between about 150° C. and about 175° C. The screw speeds may be, for example, about 50 rpm to about 100 rpm. Large scale batches may be prepared using a twin screw Buss kneader. In addition, mixing of the material may be conducted on plant scale using, for example, about a 3.5 inch (about 8.9 centimeters) diameter Buss Kneader.

In an embodiment, the intumescent plastic may be used to form fire resistant blends, wherein the fire resistant blend is a blend of the intumescent plastic and a non-intumescent polymer that is compatible with, or can be made compatible with, the intumescent plastic. If the non-intumescent polymer is not compatible with the intumescent plastic, a compatibilizing agent may be employed. As used herein, the term “compatibilizing agent” refers to those polyfunctional compounds that interact with either the intumescent plastic, the non-intumescent polymer, or both. This interaction may be chemical (e.g. grafting) or physical (e.g. affecting the surface characteristics of the dispersed phases).

Suitable non-intumescent polymers include, for example, polyethylene, polypropylene, nylon, acrylonitrile-butadiene-styrene, polyphenylene oxide, and combinations comprising at least one of the foregoing plastics.

Suitable polyethylene includes high density (HDPE, density greater than or equal to 0.941 g/cm³), medium density (MDPE, density from 0.926 to 0.940 g/cm³), low density (LDPE, density from about 0.910 to about 0.925 g/cm³) and linear low density polyethylene (LLDPE, density from about 0.910 to about 0.925 g/cm³). Furthermore, suitable polyethylenes include polyethylene homopolymers or copolymers of ethylene and C₃-C₁₀ alpha-olefin monomers. When copolymers are used, the ethylene content can be about 90 mol percent to about 100 mol percent, with the balance being made up of the C₃-C₁₀ alpha olefin.

Propylene polymers may be obtained by polymerizing monomers mainly composed of propylene. Examples of polypropylenes include a propylene homopolymer obtained by homo-polymerization of propylene, a propylene-ethylene random copolymer obtained by copolymerization of propylene and ethylene, a propylene-α-olefin random copolymer obtained by copolymerization of propylene and an α-olefin having 4 to 12 carbon atoms, and the like, and combinations comprising at least one of the foregoing polymers.

Suitable polyamides or nylons include nylon-4,6, nylon-6,6, nylon-6,10, nylon-6,9, nylon-6,12, nylon-6, nylon-11, nylon-12, 6T through 12T, 6I through 12I, and the like, and blends and copolymers and combinations comprising at least one of the foregoing polyamides.

Acrylonitrile-butadiene-styrene (ABS) graft copolymers contain two or more polymeric parts of different compositions, which are bonded chemically. The graft copolymer is preferably prepared by first polymerizing a conjugated diene, such as butadiene or another conjugated diene, with a monomer copolymerizable therewith, such as styrene, to provide a polymeric backbone. After formation of the polymeric backbone, at least one grafting monomer, and preferably two, are polymerized in the presence of the polymer backbone to obtain the graft copolymer.

The polyphenylene oxide polymers can comprising a plurality of aryloxy repeating units. Both homopolymer and copolymer polyphenylene oxides are suitable for use in the present disclosure. Suitable homopolymers are those containing, for example, 2,6-dimethyl-1,4-phenylene oxide units. Suitable copolymers include random copolymers containing such units in combination with, for example, 2,3,6-trimethyl-1,4-phenylene oxide units. Poly-(2,6-dimethyl-1,4-phenylene oxide) is an example of a suitable polyphenylene oxide.

If a compatibilizer is used, it can be, for example, copolymers, in particular block copolymers, of styrene with butadiene and, if desired, acrylonitrile. They can be copolymers of ethylene and propylene, and may contain a third monomer component, for example butadiene. Chlorinated polyethylene or ethylene-vinyl acetate copolymers are also suitable as compatibilizers, naturally depending on the particular composition of the recyclate. Other suitable compatibilizers contain, in particular, polar groups, e.g. maleic anhydride-styrene copolymers or graft polymers containing acrylic acid groups, maleic anhydride groups or glycidyl groups. The compatibilizers can be a combination comprising at least one of the foregoing compatibilizers.

The fire resistant blend can be mixed by any suitable mixing method. Such methods include solution blending or melt mixing in single or twin screw type extruders, mixing bowl, roll, kneader, or similar mixing device that can apply a shear to the components.

In an embodiment, the fire resistant blend may employ an amount of intumescent plastic or intumescent material sufficient to impart fire resistant properties to the fire resistant blend. For example, the fire resistant blend may employ about 20 wt. % to about 80 wt. % of the intumescent plastic, preferably about 20 wt. % to about 60 wt. %, and more preferably about 20 wt. % to about 40 wt. % based on the total weight of the fire resistant blend. The fire resistant blend may employ about 20 wt. % to about 80 wt. % of the non-intumescent polymer, preferably about 40 wt. % to about 80 wt. %, and more preferably about 60 wt. % to about 80 wt. % based on the total weight of the fire resistant blend. The compatibilizer, when used, may be employed in an amount less than or equal to 5 wt. %, preferably about 1 wt. % to about 5 wt. %, and more preferably about 1 wt. % to about 2 wt. % based on the total weight of the fire resistant blend. In this embodiment, the intumescent plastic may act as a carrier such that intumescence additives may readily be blended with the non-intumescent polymer to form the fire resistant blend.

In other embodiments, a fire resistant blend may be made by blending a sufficient amount of intumescence additives directly with the non-intumescent polymer to impart fire resistant properties to the fire resistant blend. In other words, an intumescent plastic is not formed as a precursor. Rather, the intumescence additives are blended with the non-intumescent polymer in a manner as described above for making the intumescent plastic. In this embodiment, the non-intumescent polymer acts as the resin matrix for the fire resistant blend.

In all of the embodiments of the fire resistant blend, the fire resistant blend employs about 10 wt. % to about 35 wt. % intumescence additives, with about 20 wt. % to about 35 wt. % preferred, wherein the weight percents are based on a total weight of the fire resistant blend. The balance of the fire resistant blend comprises a resin matrix material, e.g., high-density polyethylene, and optionally a heat stabilizer. It is further noted that the weight percents disclosed above in relation to the intumescent plastic, e.g., in Tables 1-3, can readily be adjusted such that the weight percents are based on a total weight of the fire resistant blend.

Preferably, the fire resistant blend employs greater than or equal to 65 wt. % high density polyethylene, with about 65 wt. % to about 80 wt. % preferred; and intumescent additives in an amount sufficient to impart fire resistant properties to the fire resistant blend, wherein weight percents are based on a total weight of the fire resistant blend.

The fire resistant blend can be molded into a fire resistant pallet by injection molding, extrusion, compression molding, vacuum forming, blow molding, and the like.

In another embodiment, a fire resistant laminate is disclosed, wherein the fire resistant laminate comprises layer(s) of intumescent plastic and layer(s) of non-intumescent polymer, wherein the intumescent plastic is present in an amount sufficient to impart fire resistant properties to the fire resistant blend. It is noted that the fire resistant laminate employs the same amount of intumescent material and non-intumescent polymer as disclosed above for the fire resistant blends. For example, the fire resistant laminate comprises about 20 wt. % to about 80 wt. % intumescent plastic and about 20 wt. % to about 80 wt. % non-intumescent polymer, wherein the weight percents are based on a total weight of the fire resistant laminate. In other words, the fire resistant laminate may comprise about 10 wt. % to about 35 wt. % intumescence additives, with about 20 wt. % to about 35 wt. % preferred, wherein the weight percents are based on a total weight of the fire resistant laminate.

Furthermore, it is noted that the fire resistant laminate preferably comprises greater than or equal to 65 wt. % high density polyethylene, with about 65 wt. % to about 80 wt. % preferred; and intumescent additives in an amount sufficient to impart fire resistant properties to the fire resistant blend, wherein weight percents are based on a total weight of the fire resistant laminate. It is further noted that the weight percents disclosed above in relation to the intumescent plastic, e.g., in Tables 1-3, can readily be adjusted such that the weight percents are based on a total weight of the fire resistant laminate.

The thickness of each layer in the fire resistant laminate may vary with the desired application. For example, a fire resistant laminate for use in a pallet may comprise an intumescent plastic layer having a thickness of about 1 millimeter (mm) to about 6 mm, with a thickness of about 1 mm to about 4 mm more preferred. The non-intumescent polymer preferably has a thickness of about 1.5 to 2.5 times that of the intumescent plastic layer. Furthermore, it is noted that the thickness of the plastic layer may vary based on various design criteria, e.g., the load requirement in service. In various embodiments, the plastic layer preferably has a thickness of about 4 mm to about 15 mm, with a thickness of about 4 mm to about 10 mm more preferred.

An exemplary laminate generally designated 10 is illustrated in FIG. 1. The laminate 10 comprises an intumescent plastic layer 12 and a non-intumescent polymer layer 14 disposed in physical communication with the intumescent plastic layer 12. It is noted that the intumescent plastic and the non-intumescent polymer comprise those materials discussed above.

The laminate may further comprise an adhesive layer in physical communication with the intumescent plastic layer and the non-intumescent polymer layer. Suitable adhesives, include, for example, epoxy-based adhesives, urethane-based adhesives, acrylic-based adhesives, polyvinyl acetate/urethane adhesives, polychloroprene contact adhesives, and the like and combinations comprising at least one of the foregoing adhesives. For example, a laminate generally designated 100 is illustrated in FIG. 2. The laminate 100 comprises an adhesive layer 116 disposed between an intumescent plastic layer 112 and a non-intumescent polymer layer 114.

In another embodiment, illustrated in FIG. 3, a laminate generally designated 200 comprises a first intumescent plastic layer 212, a second intumescent plastic layer 218, and a non-intumescent polymer layer 214 disposed between and in physical communication with the first and second intumescent plastic layers (212, 218). Optionally, as noted above, an adhesive layer(s) may be disposed between the intumescent each intumescent plastic layer and the non-intumescent polymer layer.

For example, a laminated generally designated 300 comprises a first intumescent plastic layer 312, a first adhesive layer 316, a non-intumescent polymer layer 314, a second adhesive layer 320, and a second intumescent plastic layer 318. More particularly, a first adhesive layer 316 is disposed between and in physical communication with first intumescent plastic layer 312 and non-intumescent polymer layer 314. Similarly, second adhesive layer 320 is disposed between and in physical communication with second intumescent plastic layer 318 and non-intumescent polymer layer 314.

It is noted that the various laminates disclosed herein may be formed as a part by, for example, co-extrusion (FIG. 2), by stacking sheets of intumescent plastic and non-intumescent polymer and molding the sheets to form a fire resistant laminate, e.g., a pallet. Suitable molding methods include, for example, injection molding, compression molding, vacuum forming, blow molding, and the like. During the molding process, the sheets develop adhesion and form a laminate. Optionally, an adhesive layer can be disposed between the intumescent plastic sheet and the non-intumescent polymer sheet prior to molding, as discussed above.

The fire resistant laminates and blends can be manufactured into fire resistant pallets. The laminates are also useful for shipping containers, school bus seats, car flooring, bulkheads, wheel wall covers, floor tile or wall tile doors, file cabinets, safes, and other applications requiring fire resistant materials. In the case of shipping pallets, a new standard for flammability of shipping pallets is under consideration by the National Fire Protection Agency. The test will be based on Underwriters Laboratory test UL 2335. The test consists of burning a stack of six 12 foot (about 3.7 meters) by 12 foot (about 3.7 meters) pallets located under a sprinkler ceiling. Criteria for evaluation include: stack stability (e.g., for 30 minutes) during the test; time for the fire to extend to the end of the array (e.g., more than 7 minutes); number of activated sprinklers (e.g., less than 14); and the maximum average temperature of a steel beam over the fire (e.g., less than 537° C.).

EXAMPLE

A pallet made of a blend of 25 wt. % intumescent plastic described above with 75 wt. % high density polyethylene, wherein weight percents are based on the total weight of the blend, was tested per UL 2335 idle pallet storage fire test. The results are discussed below. It is noted that the pallets passed the flammability test and showed excellent performance.

During the test only four sprinklers were engaged, when a total of six sprinklers were allowed. The steel beam over the fire reached a temperature of 175° F. (about 79° C.), when the temperature of about 200° F. (about 93° C.) was allowed. The temperature of the outside wall of the pallet reached a temperature of about 150° F. (about 66° C.), when a temperature of about 600° F. (about 316° C.) was allowed. After 30 minutes, the fire was extinguished. Minimal fire involvement was observed around the four gasoline soaked torches employed that were employed in the test. Most of the pallets looked like new.

Pallets made of polymers containing traditional fire retardants (e.g., halogens, phosphates, borates, and the like) are expected to fail the test because they are unable to resist large fires for long exposure times. It is expected that for such compositions, a high rate of heat release and failure to maintain stack stability will result. Furthermore, flaming melt dripping may also observed for many of those polymers. In other words, flaming melt dripping is another source of failure, since this phenomenon can lead to flame spread to neighboring materials In contrast to compositions comprising traditional fire retardants, intumescent fire resistant plastics are formulated to withstand intense fire situations for longer periods of time. The fire retardancy activity of the intumescent plastics slows down the heat release rate. In addition, they foam when exposed to fire or high temperature conditions to improve thermal insulation. Also, under fire conditions they develop a char on the surface of the part and improve resistance to burning. Intumescent plastics do not significantly melt or burn through when exposed to fire and thus can provide a fire shield.

The plastic blends and laminates disclosed herein are useful in applications where fire resistant properties are desirable. The blends and laminates are particularly useful in shipping pallet applications and have improved fire resistance as compared to other plastic pallets. In particular, pallets comprising the fire resistant blends and laminates are expected to pass the National Fire Protection Agency fire resistance standard. In addition, the disclosed fire resistant pallets are expected to be significantly less expensive than those made from polyphenylene oxide and other specialty plastics.

While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A fire resistant plastic pallet, comprising: greater than or equal to 65 wt. % high density polyethylene; and a sufficient amount of intumescence additive material to impart fire resistant properties to the fire resistant plastic pallet such that the fire resistant plastic pallet is capable of passing a fire test standard consistent with UL 2335, wherein weight percents are based on a total weight of the fire resistant plastic pallet.
 2. The fire resistant plastic pallet of claim 1, wherein the high density polyethylene is present in an amount of 65 wt. % to about 80 wt. %.
 3. The fire resistant plastic pallet of claim 1, wherein the intumescence additive material is present in an amount of about 10 wt. % to about 35 wt. %.
 4. The fire resistant plastic pallet of claim 3, wherein the intumescence additive material is present in an amount of about 20 wt. % to about 35 wt. %.
 5. The fire resistant plastic pallet of claim 1, wherein the intumescence additive material is selected from the group consisting of a gas-generating foaming agent, a char-forming agent, a filler, and combinations comprising at least one of the foregoing materials.
 6. The fire resistant plastic pallet of claim 5, wherein the gas-generating foaming agent is selected from the group consisting of ammonium dihydrogen phosphate, ammonium polyphosphate, and combinations comprising at least one of the foregoing materials.
 7. The fire resistant plastic pallet of claim 5, wherein the gas-generating foaming agent is selected from the group consisting of hydrated alumina, hydrated magnesia, melamine, and combinations comprising at least one of the foregoing materials.
 8. The fire resistant plastic pallet of claim 5, wherein the char forming agent is selected from the group consisting of monopentaerythritol, dipentaerythritol, and combinations comprising at least one of the foregoing materials.
 9. The fire resistant plastic pallet of claim 1, wherein the intumescence additive material further comprises antimony oxide, zinc borate, and combinations comprising at least one of the foregoing materials.
 10. The fire resistant plastic pallet of claim 1, wherein the fire resistant plastic pallet is made of a fire resistant blend of the high density polyethylene and the intumescence additive material.
 11. The fire resistant plastic pallet of claim 1, wherein the fire resistant plastic pallet is a fire resistant laminate.
 12. The fire resistant plastic pallet of claim 11, wherein the fire resistant laminate comprises an intumescent plastic layer disposed on a first side of a non-intumescent polymer layer.
 13. The fire resistant plastic pallet of claim 12, wherein the fire resistant laminate further comprises an adhesive layer disposed between the intumescent plastic layer and the non-intumescent polymer layer.
 14. The fire resistant plastic pallet of claim 13, wherein the fire resistant laminate further comprises a second intumescent plastic layer disposed on a second side of the non-intumescent polymer layer.
 15. The fire resistant plastic pallet of claim 12, wherein the non-intumescent layer has a thickness about 1.5 times to 2.5 times a thickness of the intumescent plastic layer.
 16. A fire resistant plastic pallet, comprising: about 65 wt. % to about 80 wt. % high density polyethylene; about 20 wt. % to about 35 wt. % intumescence additive material, wherein the intumescence additive material comprises a gas-generating foaming agent, a char-forming agent, and a filler; and wherein weight percents are based on a total weight of the fire plastic resistant pallet.
 17. The fire resistant plastic pallet of claim 16, wherein the gas-generating foaming agent is selected from the group consisting of ammonium dihydrogen phosphate, ammonium polyphosphate, and combinations comprising at least one of the foregoing materials.
 18. The fire resistant plastic pallet of claim 16, wherein the gas-generating foaming agent is selected from the group consisting of hydrated alumina, hydrated magnesia, melamine, and combinations comprising at least one of the foregoing materials.
 19. The fire resistant plastic pallet of claim 16, wherein the char forming agent is selected from the group consisting of monopentaerythritol, dipentaerythritol, and combinations comprising at least one of the foregoing materials.
 20. The fire resistant plastic pallet of claim 16, wherein the intumescence additive material further comprises antimony oxide, zinc borate, and combinations comprising at least one of the foregoing materials. 